Digital codecs of the type MP3 or other formed by a standard encoder makes it possible to encode, according to a known encoding protocol, digital stereo sound signals for example in WAVE format in order to transform said digital stereo sound signals into encoded stereo signals; a standard decoder is also known which makes it possible to decode, according to a known decoding protocol, encoded stereo signals in order to transform them into digital stereo signals for example in WAVE format. In general, encoding consists in compressing stereo signals, while decoding consists in decompressing compressed stereo signals.
The problem is that the transmission channel available for encoding is generally limited to N kbits/s (N generally being equal to 64 or 128). However when a stereo signal formed of two audio channels: a right sound channel and a left sound channel, is encoded according to the characteristics of the codecs used, it can be necessary to encode approximately each audio channel of the signal at a transfer rate of N/2 kbits/s.